(1) Field of The Invention
This invention relates to the local defocus, within an image field, for photolithographic patterns on integrated circuit wafers, and more particularly to a method and system for real time detection of local defocus problems.
(2) Description of The Related Art
Photolithographic processing is critical to the fabrication of integrated circuit wafers. In the photolithographic processing operations a key step is that of focussing a pattern on a layer of photoresist. Lack of focus of the image degrades the accuracy of the pattern transferred to the photoresist. Local defocus caused by such problems as lack of planarity of the photoresist surface is an important problem in photolithographic processing.
U.S. Pat. No. 5,563,684 to Stagaman describes an adaptive wafer modulator to elastically deform the exposure area of the wafer to correct for lack of planarity of the un-deformed wafer surface.
U.S. Pat. No. 5,828,455 to Smith et al. describes methods of measurement and data analysis for correction of an optical system used in forming images in a layer of photoresist.
U.S. Pat. No. 5,202,748 to MacDonald et al. describes an in-situ process control system for controlling the focus of photolithographic steppers.
U.S. Pat. No. 4,758,094 to Wihl et al. describes a process and apparatus for in-situ qualifying a reticle or master pattern used in patterning systems.
U.S. Pat. No. 5,773,315 to Jarvis describes a method of predicting yields for processes having two or more masking steps.